Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure to radiation.
This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the coated surface of the substrate.
There are two types of photoresist compositions, negative-working and positive-working. When negative-working photoresist compositions are exposed image-wise to radiation, the areas of the resist composition exposed to the radiation become less soluble to a developer solution (e.g. a cross-linking reaction occurs) while the unexposed areas of the photoresist coating remain relatively soluble to such a solution. Thus, treatment of an exposed negative-working resist with a developer causes removal of the non-exposed areas of the photoresist coating and the creation of a negative image in the coating. Thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited.
On the other hand, when positive-working photoresist compositions are exposed image-wise to radiation, those areas of the photoresist composition exposed to the radiation become more soluble to the developer solution (e.g. a rearrangement reaction occurs) while those areas not exposed remain relatively insoluble to the developer solution. Thus, treatment of an exposed positive-working photoresist with the developer causes removal of the exposed areas of the coating and the creation of a positive image in the photoresist coating. Again, a desired portion of the underlying substrate surface is uncovered.
After this development operation, the now partially unprotected substrate may be treated with a substrate-etchant solution or plasma gases and the like. The etchant solution or plasma gases etch that portion of the substrate where the photoresist coating was removed during development. The areas of the substrate where the photoresist coating still remains are protected and, thus, an etched pattern is created in the substrate material which corresponds to the photomask used for the image-wise exposure of the radiation. Later, the remaining areas of the photoresist coating may be removed during a stripping operation, leaving a clean etched substrate surface. In some instances, it is desirable to heat treat the remaining photoresist layer, after the development step and before the etching step, to increase its adhesion to the underlying substrate and its resistance to etching solutions.
Positive working photoresist compositions are currently favored over negative working resists because the former generally have better resolution capabilities and pattern transfer characteristics. Photoresist resolution is defined as the smallest feature which the resist composition can transfer from the photomask to the substrate with a high degree of image edge acuity after exposure and development. In many manufacturing applications today, resist resolution on the order of less than one micron are necessary. In addition, it is almost always desirable that the developed photoresist wall profiles be near vertical relative to the substrate. Such demarcations between developed and undeveloped areas of the resist coating translate into accurate pattern transfer of the mask image onto the substrate. This becomes even more critical as the push toward miniaturization reduces the critical dimensions on the devices.
Photosensitive compositions are currently used in microlithography to form integrated circuits. As the requirement for faster integrated circuits grows, so does the need to reduce the dimensions of the features printed on these circuits. One method of producing small features is to imagewise irradiate the photoresist with light of shorter wavelengths. The traditional photosensitive compositions which contained novolaks as resins and diazonaphthoquinones as photosensitive compounds worked well at wavelengths between 350 nm and 450 nm. Diazonaphthoquinone photoactive compounds used for irradiation wavelengths between 350 nm and 450 nm are known and described in the following patents, U.S. Pat. No. 4,588,670, U.S. Pat. No. 4,853,315, U.S. Pat. No. 5,501,936, U.S. Pat. No. 5,532,107 and U.S. Pat. No. 5,541,033, which are incorporated herein by reference. However, with light of wavelengths less than 350 nm, and especially less than 250 nm, neither do the typical novolacs have sufficient transparency, nor do the diazonaphthoquinones have the necessary absorption characteristics to allow for photoresist images of adequate resolution and edge acuity to be formed. Therefore, it has become necessary to synthesize new resins and new photoactive compounds for use at shorter wavelengths.
Radiation-sensitive mixtures containing photoactive diazo derivatives which are suitable for irradiation with high-energy deep UV radiation have been described in the literature for some time.
U.S. Pat. No. 4,339,522 discloses positive-working radiation-sensitive mixtures which contain, as a photoactive compound, a diazo derivative of Meldrum's acid. This compound is said to be suitable for exposure to high-energy deep UV radiation in the range between 200 and 300 nm. However, this photoactive compound is lost under the elevated processing temperatures frequently employed in practice; the radiation-sensitive mixture loses its original activity, so that reproducible photoresist images are not obtained.
Further, positive-working photoactive compounds which are sensitive in the deep UV region are disclosed in U.S. Pat. No. 4,735,885. The compounds have the disadvantage that the carbenes formed from these on exposure do not have adequate stability in the matrix for the desired formulation of carboxylic acid. This results in an inadequate solubility difference between the exposed and the unexposed areas in the developer and thus leads to an undesirably high removal rate of the unexposed areas, leading to poor resolution.
U.S. Pat. No. 4,622,283 provide 2-diazocyclohexane- 1,3-dione or -cyclopentane-1,3-dione derivatives as photoactive compounds for radiation-sensitive mixtures of the type described. These compounds have lower volatility, but they exhibit, depending on the substitution pattern present, poor compatibility in the radiation-sensitive mixture. This can cause recrystallization in the solution or in the coating.
EP-A 0 195 986 proposes phosphoryl-substituted diazocarbonyl compounds as photoactive compounds, since these have a higher carbene stability. In practice, however, such compounds will probably not be widely accepted since phosphorus atoms are potentially used as dopants for the semiconductor substrates.
Photoactive compounds based on 3, diazo 4, oxo coumarin structure and sensitive in the shorter wavelengths are disclosed in JP 2,061,640. Additionally, JP 3,079,670, describes a photoresist based on a similar coumarin structure, and further includes 2-diazo 1-indanone and 3-diazo 2,4-quinolinedione as photosensitive compounds, wherein the photoresist when processed gives a negative image. These are monomeric diazo compounds that have substituents of low molecular weight, such as methyl, chlorine, methoxy, propyl, that can be susceptible to volatility, diffusion through the photoresist film, amongst other factors. Furthermore, the 3-diazo 2,4-quinolinedione described in JP 3,079,670 discloses as substituents only sulfonic acid, sulfonyl halogeno, alkoxy, hydrogen or halo groups, which in a photoresist, give a negative image.
All of the references mentioned herein are incorporated by reference in their entirety.
The present invention describes a positive photosensitive composition comprising an alkali soluble resin, a novel photoactive compound based on the structure: ##STR2## where, X is O, S or N--R', where R' is H, alkyl, substituted alkyl, aryl or aralkyl,
Y is a connecting group such as SO.sub.2, CO, O or NR', PA1 Z is a carbon containing organic ballast moiety having a molecular weight greater than about 75 and can form a bond with the connecting group, PA1 R is independently H, alkyl, alkoxy, aryl, aralkyl, halo or fluoroalkyl, PA1 m=1-3, and n.gtoreq.1; PA1 Y is a connecting group such as SO.sub.2, CO, O or NR', PA1 Z is a carbon containing organic ballast moiety having a molecular weight greater than about 75 and can form a bond with the connecting group, PA1 R is independently H, alkyl, alkoxy, aryl, aralkyl, halo or fluoroalkyl, PA1 m=1-3, and n.gtoreq.1; PA1 Y is a connecting group such as SO.sub.2, CO, O or NR', PA1 Z is a carbon containing ballast moiety having a molecular weight greater than about 75 and can form a bond with the connecting group, PA1 R is independently H, alkyl, alkoxy, aryl, aralkyl, halo or fluoroalkyl, PA1 m=1-3, and n.gtoreq.1; PA1 where where R.sub.1 to R.sub.5 are independently alkyl having greater than 6 carbon atom, aryl or aralkyl and n is the degree of diazotization.
and a solvent or mixture of solvents. The novel compound is not a low molecular weight diazo, has high decomposition temperature, good absorption characteristics and unexpectedly when formulated in to a photoresist gives a positive photoresist image.